Paolo Gambino Beauty 2005 Assisi 1 Semileptonic and radiative B decays Paolo Gambino INFN Torino.
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Transcript of Paolo Gambino Beauty 2005 Assisi 1 Semileptonic and radiative B decays Paolo Gambino INFN Torino.
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 Paolo Gambino Beauty 2005 Assisi 1 Semileptonic and radiative B decays Paolo Gambino INFN Torino
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 Paolo Gambino Beauty 2005 Assisi 2 A set of interdependent measurements b c l treeBR~10%V cb  b u l tree~10 3 V ub  b s loop~3 10 4 new physics, V ts  b d loop~ 10 6 new physics, V td  There are also b s,dl + l  to complement the radiative modes Not only BR are relevant: various asymmetries, spectra etc
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 Paolo Gambino Beauty 2005 Assisi 3 What do they have in common? INCLUSIVEEXCLUSIVE OPE: nonpert physics described by B matrix elemnts of local operators can be extracted by exp suppressed by 1/m b 2 Form factors: in general computed by non pert methods (lattice, sum rules,...) symmetry can provide normalization Simplicity: ew or em currents probe the B dynamics B X Simplicity is almost always destroyed in practical situations...
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 Paolo Gambino Beauty 2005 Assisi 4 EXCLUSIVE Determination of A V CKM A can be determined using V cb  or V ts  Two roads to V cb  INCLUSIVE
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 Paolo Gambino Beauty 2005 Assisi 5 V cb  from B D * l At zero recoil, where rate vanishes. Despite extrapolation, exp error ~ 2% Main problem is form factor F(1) The nonpert quantities relevant for excl decays cannot be experimentally determined Must be calculated but HQET helps. Lattice QCD: F(1) = 0.91 +0.03 0.04 Sum rules give consistent results Needs unquenching (under way) Even slope may be calculable... F B D * (1) = A [1  O(1/m b,1/m c ) 2 ] B Dl gives consistent but less precise results; lattice control is better V cb /V cb ~ 5% and agrees with inclusive det, despite contradictory exps THE NONPERT UNKNOWNS MUST BE CALCULATED, CANNOT BE MEASURED B D*D* bc d l v
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 Paolo Gambino Beauty 2005 Assisi 6 The advantage of being inclusive QCD m b : inclusive decays admit systematic expansion in QCD /m b Nonpert corrections are generally small and can be controlled Hadronization probability =1 because we sum over all states Approximately insensitive to details of meson structure as QCD m b (as long as one is far from perturbative singularities) s and can be expressed as double series in s and QCD /m b (OPE) with parton model as leading term No 1/m b correction!
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 Paolo Gambino Beauty 2005 Assisi 7 HQE = Heavy Quark Expansion A double expansion can be expressed in terms of structure functions related to Im of OPE (HQE): The leading term is parton model, c i are series in s New operators have nonvanishing expection values in B and are suppressed by powers of the energy released, E r ~ m b m c No 1/m b correction! OPE predictions can be compared to exp only after SMEARING and away from endpoints: they have no LOCAL meaning
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 Paolo Gambino Beauty 2005 Assisi 8 Leptonic and hadronic spectra Total rate gives CKM elmnts; global shape parameters tells us about B structure OPE predictions can be compared to exp only after SMEARING and away from endpoints: they have no LOCAL meaning
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 Paolo Gambino Beauty 2005 Assisi 9 heavy quark masses must be carefully defined: short distance, low scale State of the art Known corrections up to 1/m b 3 : OPE/HQE predictions are only functions of possible cuts and of 1, 2 O(1/m b 2 ): mean kin.energy of b in B
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 Paolo Gambino Beauty 2005 Assisi 10 State of the art Known corrections up to 1/m b 3 : OPE/HQE predictions are only functions of possible cuts and of 1, 2 Gremm,Kapustin... 1,21,2 O(1/m b 2 ): mean kin.energy of b in B
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 Paolo Gambino Beauty 2005 Assisi 11 Perturbative Corrections: full O( s ) and O( 0 s 2 ) available For hadronic moments thanks to NEW calculations Trott Aquila,PG,Ridolfi,Uraltsev Recent implementation for moments of lept and hadronic spectra including a cut on the lepton energy Bauer et al.,Uraltsev & PG State of the art Known corrections up to 1/m b 3 : OPE/HQE predictions are only functions of possible cuts and of 1, 2 Gremm,Kapustin... 1,21,2
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 Paolo Gambino Beauty 2005 Assisi 12 Using moments to extract HQE parameters Central moments can be VERY sensitive to HQE parameters Experiments at (4s) require a CUT on the lepton energy E l >0.61.5 GeV. Provided cut is not too severe (~1.3GeV) the cut moments give additional info We do know something on HQE par. need to check consistency. M B* M B fix G 2 = 0.350.03 Sum rules: G 2 2, D 3  3 LS... BUT: OPE accuracy deteriorates for higher moments (getting sensitive to local effects) Variance of mass distribution
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 Paolo Gambino Beauty 2005 Assisi 13 Global fit to  V cb , BR sl, HQE parmts Pioneer work by CLEO & Delphi employed less precise/complete data, some external constraints, and CLEO a different scheme Not all points included No external constraint LEPTONIC MOMENTS Preliminary, O.Buchmuller
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 Paolo Gambino Beauty 2005 Assisi 14 Global fit to  V cb , BR sl, HQE parmts HADRONICMOMENTS Preliminary, O.Buchmuller Excellent agreement within exp and TH errors Very similar results in a different approach/scheme, Bauer et al
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 Paolo Gambino Beauty 2005 Assisi 15 H.Flaecher, CKM 2005
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 Paolo Gambino Beauty 2005 Assisi 16 Bauer, Manohar, Ligeti, Luke, Trott 2005 Results in the 1S scheme There are several differences: perturbative quark mass scheme expansion in inverse powers of m c handling of higher orders estimate of th errors...
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 Paolo Gambino Beauty 2005 Assisi 17 +unquenching
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 Paolo Gambino Beauty 2005 Assisi 18 Theoretical uncertainties are crucial for the fits Missing higher power corrections Intrinsic charm Missing perturbative effects in the Wilson coefficients: O( s 2 ), O( s /m b 2 ) etc Duality violations How can we estimate all this? Different recipes, results for V cb  unchanged
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 Paolo Gambino Beauty 2005 Assisi 19 Testing partonhadron duality What is it? What is it? For all practical purposes: the OPE. No OPE, no duality Do we expect violations? Do we expect violations? Yes, problems prevalently arise because OPE must be continued analytically. there are effects that cannot be described by the OPE, like hadronic thresholds. Expected small in semileptonic decays Can we constrain them effectively? Can we constrain them effectively? in a selfconsistent way: just check the OPE predictions. E.g. leptonic vs hadronic moments. Models may also give hints of how it works Caveats? Caveats? HQE depends on many parameters and we know only a few terms of the double expansion in s and /m b.
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 Paolo Gambino Beauty 2005 Assisi 20 It is not just V cb... HQE parameters describe universal properties of the B meson and of the quarks c and b masses can be determined with competitive accuracy (likely better than 70 and 50 MeV) m b m c is already measured to better than 30 MeV: a benchmark for lattice QCD etc? It tests the foundations for inclusive measurements most V ub incl. determinations are sensitive to a shape function, whose moments are related to 2 etc, Bounds on , the slope of IW function (B D * form factor)... Need precision measurements to probe limits of HQE & test our th. framework
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 Paolo Gambino Beauty 2005 Assisi 21 V ub  is the priority now = 0.210 0.035 = 0.339 0.021 http://www.utfit.org
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 Paolo Gambino Beauty 2005 Assisi 22 Strictly tree level
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 Paolo Gambino Beauty 2005 Assisi 23 b ulv exclusive (CLEO only) There is NO normalization of form f.s from HQ symmetry New first unquenched results lattice errors still ~15% Sum rules good at low q 2 lattice at high q 2 : complement each other Lattice (distant) goal is 56% New strategy using combination of rare B,D decays Grinstein& Pirjol
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 Paolo Gambino Beauty 2005 Assisi 24 V ub  (not so much) inclusive V ub  from total BR(b ul ) almost exactly like incl V cb  but we need kinematic cuts to avoid the ~100x larger b cl background: m X (M B 2 M D 2 )/2M B q 2 > (M B M D ) 2... or combined (m X,q 2 ) cuts The cuts destroy convergence of the OPE, supposed to work only away from pert singularities Rate becomes sensitive to local bquark wave function properties (like Fermi motion at leading in 1/m b SHAPE function)
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 Paolo Gambino Beauty 2005 Assisi 25 Luke, CKM workshop 2005
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 Paolo Gambino Beauty 2005 Assisi 26 Each strategy has pros and cons Luke, CKM workshop 2005
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 Paolo Gambino Beauty 2005 Assisi 27 What do we know about f(k + )? Its moments can be expressed in terms of m.e. of local operators, those extracted from the b>c moments It can be extracted from b s (see later) It can also be studied in b ulv spectra (see next) It gets renormalized and we have learned how (delicate interplay with pert contributions)
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 Paolo Gambino Beauty 2005 Assisi 28 V ub incl. and exclusive exclusive Intense theoretical activity: subleading shape functions optimization of cuts (P +,P  etc) weak annihilation contribs. Resum. pert. effects relation to b s spectrum SCET insight A lot can be learned from exp (on shape function from b s , WA, indirect constraints on s.f., subleading effects from cut dependence,...) REQUIRES MANY COMPLEMENTARY MEASUREMENTS (affected by different uncert.) There is no Best Method WE ARE ALREADY AT 10% New BRECO analyses; new results soon...
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 Paolo Gambino Beauty 2005 Assisi 29 Cutting the cuts... New exp analyses based on fully reconstructed events allow high discri mination of charmed final states 2004 Unfolded M X spectrum Babar measured M X moments. Results can be improved by cutting in a milder way than usual Its time to start using b>u data to constrain sf! Useful to validate theory and constrain f(k + ) & WA PG,Ossola,Uraltsev
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 Paolo Gambino Beauty 2005 Assisi 30 b s transitions Inclusive decays are described by OPE (except charm loop contributions!) QCD m b M W m b M W Large L=log m b /M W must be resummed. LO: s n L n, NLO: s n L n1 But many more operators appear adding gluons Tower of local ops OPE bRbR sLsL The current is not conserved and runs between M W and m b We have AT LEAST 3 scales
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 Paolo Gambino Beauty 2005 Assisi 31 The main ingredients Process independent: The Wilson coefficients C iThe Wilson coefficients C i (encode the short distance information, initial conditions) The Anomalous Dimension MatrixThe Anomalous Dimension Matrix (mixing among operators, determines the evolution of the coefficients, allowing to resum large logs) Process dependent: Process dependent: matrix elements B X s B X s : NLO QCD calculation completed, all results checked, EW, power corrections B X s ll: B X s ll: NNLO & EW calculation just completed,power corrections c
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 Paolo Gambino Beauty 2005 Assisi 32 The charm mass problem m c enters the phase factor due to normalization = 0.5810.017 and the NLO matrix elements As the related LO diagrams vanish, the definition of m c is a NNLO issue. Numerically very important because these are large NLO contributions: m c (m c )=1.250.10 GeV m c (m b )=0.850.11 GeV m c (pole)~1.5GeV But pole mass has nothing to do with these loops Changing m c /m b from 0.29 (pole) to 0.22 (MSbar) increases BR by 11% gives DOMINANT 6% theory error 0.22 0.04 gives DOMINANT 6% theory error Misiak & PG
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 Paolo Gambino Beauty 2005 Assisi 33 Error anatomy of BR Total error 8% dominated by charm mass Can be partially resolved by NNLO Update under way Misiak, PG 2001
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 Paolo Gambino Beauty 2005 Assisi 34 Photon spectrum vs total BR The OPE does not predict the spectrum, only its global properties: the higher the cut the higher the uncertainty Conversely, constraining the HQE parameters constrains the possible shape functions Possible subleading shape functns effects in V ub applications The shape function gets renormalized by perturbative effects: some complications may be better understood in SCET (Bauer & Manohar, Neubert et al)
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 Paolo Gambino Beauty 2005 Assisi 35 Universality: spectrum of B X s Motion of b quark inside B and gluon radiation smear the spike at m b /2 Belle: lower cut at 1.8GeV The photon spectrum is very insen sitive to new physics, can be used to study the B meson structure = m b /2 +... var = 2 /12+... Importance of extending to E min ~ 1.8 GeV or less for the determination of both the BR AND the HQE parameters Bigi Uraltsev Info from radiative spectrum compatible with semileptonic moments s quark b quark
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 Paolo Gambino Beauty 2005 Assisi 36 results in two different schemes, agree well with b>clv
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 Paolo Gambino Beauty 2005 Assisi 37 More cuts complications hh ii 00 h ~m b i ~m b 0 ~=m b 2E cut The lower photon energy cut E cut introduces two new scales EVEN when local OPE works fine terms s () could be large nonpert domain Neubert 2004
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 Paolo Gambino Beauty 2005 Assisi 38 Neubert (II) Need to disentangle 3 scales MultiScaleOPE QCD SCET HQET local OPE hh ii 00 How well can we predict the radiative tail? Neubert finds F(E >1.8GeV)=0.89 0.07, BR 3% lower, and theory error on BR 50% larger FUNDAMENTAL LIMITATION? Main effect due to pert corrections whose scale is determined by higher orders (BLM etc): NNLO is the solution (at least to large extent) Sudakov resummation is irrelevant for E cut
 Paolo Gambino Beauty 2005 Assisi 41 b>sl + l  : a more complicated case This decay mode is sensitive to different operators, hence to different new physics Here large logs are generated even without QCD: LO s n L n+1, NLO s n L n,... However, numerically the leading log is subdominant, yielding an awkward series: in BR 1+ 0.7 ( s ) + 5.5 ( s 2 ) +...
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 Paolo Gambino Beauty 2005 Assisi 42 Error Anatomy for BR ll M top dominant error 7% scale uncertainty 5% m b pole = 4.800.15 GeV 5% phase space factor 3% No m c issue as charm enters at LO TOTAL ERROR ~10% BUT: BUT: bottom uncertainty is not a fundamental limitation m b short distance 3050 MeV simply change scheme! EXP: only inclusive rate, Belle (140fb 1) : (4.40.80.8)x10 6 Babar(80fb 1 ): (5.61.51.3)x10 6 We get (4.60.8)x10 6 (m ll >0.2GeV) Bobeth,PG,Gorbahn,Haisch
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 Paolo Gambino Beauty 2005 Assisi 43 the UT from excl radiative decays Inclusive b>d experimentally impossible, but exclusive modes start being accessible Ratios of B / B K * allow a determination of V td / V ts  that is independent of form factors in the limit of SU(3) Calculations rely on QCD factorization and on lattice/sum rules for the estimate of SU(3) violation (Beneke et al, Bosch Buchalla) power corrections apparently suppressed Neutral modes dont have WA, =1.2 0.1 (CKM 2005) LC sum rules errors large, Lattice calculations only exploratory
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 Paolo Gambino Beauty 2005 Assisi 44 An interesting deviation? Impact on UT using only neutral modes: BR(B 0 0 )=0.6 +1.9 1.4 x10 7 Impact on UT using average of neutral and charged modes: BR(B / )=(6.4 2.7) x10 7
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 Paolo Gambino Beauty 2005 Assisi 45 Summary of main theory limitations processquantityTh errorneedsgoal BD * lv V cb  ~4% New lattice results 1% BXlv V cb  ~1.5% New pert calculations